SU1427264A1 - Method of modulation-phase detection of epr signals - Google Patents

Abstract

The invention relates to technical physics and can be used in the development of equipment for the study of substances by the EPR and DEAR methods. The purpose of the invention is to increase the sensitivity and expand the range of measured relaxation parameters. The sample is placed in a dual-frequency resonator 4 microwave transmission type. The modulation frequency of the magnetic field is set equal to the difference between the frequencies of the oscillation modes of the resonator 4. Sample 5 is exposed to the microwave field of the generator 3 at the frequency of the first mode of oscillation of the resonator 4. The EPR signal is measured by the induction signal at the frequency of the second mode of the resonator 4 and the detector Its phase detection is relative to the microwave frequency of the generator 3. 3 sludge. (L tc h tc o

Description

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The invention relates to technical physics and can be used in the development of spectrometric equipment for the study of paramagnetic substances by electron paramagnetic resonance (EPR) and double electron nuclear resonance methods.

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The purpose of the invention is to increase the sensitivity and expand the range of measured relaxation parameters.

FIG. 1 shows a block diagram of a device for modulating phase recording of EPR signals implementing the proposed method; figure 2 is a variant of the design of a bimodal dual-frequency microwave resonator pass

foot type; FIG. 3 — O — and 90 — the components of the EPR signal of a sample of a digitized chimeric acid wave, measured by the proposed method at a modulation frequency of 100 MHz.

The device for modulating-phase registration of EPR signals contains an electromagnet 1 with a control unit 2, a microwave generator 3 connected to the input of a through-pass measuring resonator 4 with the sample under study 5, a microwave detector 6, the first input of which is connected to the output of the measuring resonator 4 , and the second through the directional coupler 7 - to the output of the microwave generator 3, the modulator 8 of the magnetic field with the coils 9 of modulation. , At the output of the microwave detector 6, a synchronous detector 10 is turned on, whose reference input is connected via a 90 phase converter I1 to the second output of the modulator 8.

The registration of the ESR signals is carried out as follows.

As in the known method, the relaxation parameters of paramagnetic substances are measured by the modulation-phase method. The polarizing magnetic field at the location of the sample 5 is modulated with a frequency of 5 close to the inverse of the relaxation time T of the sample under study 5. In the EPR signal, a phase delay LF occurs at the modulation frequency, the value of which is proportional to the relaxation time (tg. I) Amount of delay. The frequency g is determined from the 90 components of the EPR signal.

The source of the polarizing magnetic field is the electromagnet 1. The magnitude of the polarizing magnetic field is controlled by the control unit 2.

five

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five

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five

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and modulated by modulation coils 9 connected to the output of the modulator 8. At the second output of the modulator 8, a reference signal is generated, which is fed to the reference input of the synchronous detector 10 through the phase shifter 11.

When the condition of resonance is fulfilled, where is the hygromagnetic ratio; And - the value of the polarizing magnetic field; and) is the frequency of the SEC, absorption and simultaneous radiation of the microwave power of samples 5 occurs, i.e. an absorption signal and an EPR magnetic induction signal are observed. The intensities of the absorption and induction signals are approximately equal, since the probabilities of forced quantum transitions of electrons with energy absorption and emission are equal.

In the proposed method, the EPR signal is recorded by the induction method. When a polarizing and superhigh-frequency magnetic fields are applied to the test sample 5, the microwave power emitted by the sample 5 at the time of resonance is measured.

The paramagnetic sample under study is placed in a pass-through microwave frequency resonator (Fig. 2). Two modes of microwave oscillations can simultaneously exist in a resonator — of the type with a frequency W and of the type Ncx with a frequency of uij. which are independent of mutual orthogonality and difference in oscillation frequencies (lA g). The sample 5 is located in the cavity of the resonator 4 at the maximum of the magnetic component of the microwave field of each of the oscillation modes. .

The superhigh-frequency magnetic field acting on the examined o, b-sample 5, is excited in the measuring resonator 4 at the frequency tJ of the first oscillation mode. The microwave power frequency and) is fed to the input of the resonator 4 through the communication hole from the output of the microwave generator 3.

When specifying the conditions for recording the EPR signal, the values of the resonant frequencies u) and. measuring resonator 4 is selected based on a predetermined modulation frequency. The difference between the frequencies o) and the oscillation modes of the measuring resonator 4 must be equal to the frequency 9 of the modulation: t A.,

High frequency modulating magnetic field modulates resonances.

This results in modulation of the microwave power absorbed and emitted by the sample 5, which is modulated with the frequency usr. Three spectral components are observed in the spectrum of the EPR signal at the microwave frequency: central (with a frequency A equal to the resonance excitation frequency) and two lateral components in phase by 90. At the exit syno

The chronic detector 10 forms a 90-component EPR signal.

In the proposed method, the modulation frequency is not superimposed on the limitations associated with the bandwidth of the measuring resonator. Separation of spectral components

(with frequencies c4 + 5 and iJi-jp) .Info-IQ microwave power of the EPR signal for various

the lateral components are compounded, and their amplitudes are equal; therefore, only one side component is measured to register the modulation-phase EPR signal. The first side component of the EPR signal has a frequency i), equal to the frequency u) g of the second oscillation mode of the measuring resonator 4, therefore the 9PR induction signal emitted by sample 5 excites the oscillations of the second mode in the resonator 4. The other side component of the EPR signal has a frequency i) -i, which differs from the resonant frequencies by the resonance modes of the resonator, which allows using practically high modulation frequencies. In this case, it is only necessary to ensure equality of the modulation frequency and the frequency difference between the two-frequency resonator.

The proposed method allows to increase the sensitivity in the study of substances with short (shorter

2Q 10 c) relaxation parameters, there is no need to reduce the Q-factor of the measuring resonator to provide it with a wide bandwidth, but on the contrary, it is better to use the phase outlined by 90. At the exit syno

The chronic detector 10 forms a 90-component EPR signal.

In the proposed method, the modulation frequency is not superimposed on the limitations associated with the bandwidth of the measuring resonator. Separation of spectral components

The modes of oscillation of the resonator allows the use of practically high modulation frequencies. In this case, it is only necessary to ensure equality of the modulation frequency and the frequency difference between the two-frequency resonator.

The proposed method allows to increase the sensitivity in the study of substances with short (shorter

10 c) relaxation parameters, there is no need to reduce the Q-factor of the measuring resonator to provide it with a wide bandwidth; on the contrary, it is better to use high

4, and is suppressed by resonator 4. 25 code-measuring two-frequency measurement. Thus, in the proposed resonant resonator, which will provide the maximum (the same as in the known method at low modulation frequencies)

The effect on sample 5 by a microwave magnetic field is carried out at a frequency (D of the first mode of oscillation of the measuring resonator 4, and the EPR signal Q is measured at the frequency u) - (D St of the second mode of oscillation of the resonator 4. At the same time, even at very high frequencies the EPR signal in the cavity 4 is not suppressed.

The EPR signal at the modulation frequency d is obtained by phase detection of the EPR induction signal (at frequency u) relative to the action of a microwave magnetic field (sample (D)) on sample 5. For this, the induction signal at the frequency CO of the second mode of oscillation through the communication hole is supplied from the output of the resonator 4 to the input of the microwave detector 6. The microwave power (having a sl) frequency is required for biasing the detector 6) is selected by the directional coupler 7 from the output The microwave generator 3 is fed to the second input of the microwave detector 6. At the output of the detector 6, an ESR signal is generated at the modulation frequency Sc.

The EO-component of the EPR signal is generated by synchronous detection40

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sensitivity of the EPR spectrometer.

Fig. 3 shows the O -. Spectra and 90 - components of the EPR signal of a sample of a digit-ferrite sand screen, measured using the proposed method at a modulation frequency of 100 MHz. The spectra were measured at a SECh power of 0.5 mW, a modulation amplitude of 0.5 Oe, and a frequency difference between the modes of the measuring bimodal resonator 100 MHz. The spin-spin relaxation time of paramagnetic centers is 5.1-10 s.

Claims (1)

The invention method of modulation-phase recording of EPR signals, including the impact on the sample under investigation by microwave (microwave), polarizing and modulating magnetic fields and measuring 90 components of the EPR signal at the modulation frequency, which is increasing the sensitivity and expanding the range of measured relaxation parameters, the sample under study is placed in a bimodal two EPR signal at the modulation frequency. - the microwave frequency resonator For this, the signal from the output of the microwave detector 6 is fed to the input of the synchronous detector 10, to the reference input of which a modulation signal is received, double-type, the microwave frequency is applied to the frequency of the first mode of the microwave resonator, the frequency of the modulating magQe ; 0 five 0 sensitivity of the EPR spectrometer. Fig. 3 shows the O -. Spectra and 90 - components of the EPR signal of a sample of a digit-ferrite sand screen, measured using the proposed method at a modulation frequency of 100 MHz. The spectra were measured at a SECh power of 0.5 mW, a modulation amplitude of 0.5 Oe, and a frequency difference between the modes of the measuring bimodal resonator 100 MHz. The spin-spin relaxation time of paramagnetic centers is 5.1-10 s. The invention method of modulation-phase recording of EPR signals, including the impact on the sample under investigation by microwave (microwave), polarizing and modulating magnetic fields and measuring 90 components of the EPR signal at the modulation frequency, which is increasing the sensitivity and expanding the range of measured relaxation parameters, the sample under study is placed in a bimodal two-frequency microwave pass-through resonator type, the effect of a microwave magnetic field is carried out. at the frequency of the first mode of oscillation of the microwave resonator, the frequency of the modulating magnetic FIELD is set equal to the difference between the frequencies of the modes of oscillations of the microwave resonator and the signal of the EPR induction is measured at the frequency of the second mode of oscillation of the microwave resonator EPR signal on I  BUT city /. FIG. 2 the modulation frequency is obtained by phase detection of the EPR induction signal relative to the frequency of the microwave magnetic field acting on the sample under study.